firewalk - 5.0-5 main

Firewalk is an active reconnaissance network security tool that attempts to
determine what layer 4 protocols a given IP forwarding device will pass. It
works by sending out TCP or UDP packets with a TTL one hop greater than the
targeted gateway. If the gateway allows the traffic, it will forward the
packets to the next hop where they will expire and elicit an ICMP_TIME_EXCEEDED
message. Otherwise, it will likely drop the packets and there will be no
response.
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To get the correct IP TTL that will result in packets expiring one hop beyond
the gateway, Firewalk needs to ramp up hop counts. It does this in the same
manner that traceroute works. Once the scan is `bound` (that is, Firewalk
knows the gateway hop count), it begins the scan. The ultimate destination host
does not have to be reached, it only needs to be somewhere downstream, on the
other side of the gateway, from the scanning host.
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Firewalk helps in assessing the security configuration of packet filtering
devices, such as those used in firewall systems. It is relevant for network
security assessments, like network penetration tests (pentests).